Drilling and production platforms, e.g. for the recovery of fossil-fuel material, for example, petroleum and natural gas, are frequently anchored to a support structure previously affixed in the sea bottom. Such platforms may be formed as semi-submersible sea-going vessels which can carry the drilling rig or production equipment and are adapted to be partially submerged in the sea and securely affixed to the substructure or support.
The support generally comprises a plurality (usually three) columns or posts which have previously been anchored in the sea bed and which are adapted to be affixed to the platform at their upper end.
Problems have been encountered heretofore in attaching the floating platform to such support posts. The platforms are relatively massive and the movements imparted thereto by the sea generate significant kinetic energy which, during the attachment phase, is frequently transmitted to the posts causing residual deformation or damage to the post or attachment structure.
When the platform is a semi-submersible sea-going vessel, the rise and fall of the level of the sea, the pitch, roll and yaw movements of the platform all impede effective attachment to the supports.
The problem is made more difficult in that the devices which are provided in conventional systems to absorb the high kinetic energy of the platform frequently must also be capable of taking up the full static load. The stresses applied during attachment and thereafter alternately increase and decrease with the sea movements and transmission to the support of these stresses must be prevented by rapid accommodation of the cushioning devices to them.
In spite of the interposition of deformable elements in the form of elastically extendable members or plastically or elastically compressible support cups, the difficulties mentioned above have prevailed to this date and it has been possible to secure a drilling or production platform to the columns in a manner sufficient to withstand environmental extremes only with the greatest difficulty and at relatively high cost.
The attachment devices and cushioning arrangements used heretofore have required constant maintenance and high capital expenditure. In spite of all precautions, moreover, weather extremes have caused failure with serious consequences to the platform and operating personnel, with conventional arrangements.